Portable machine tools for machining tubular workpieces such as pipes typically include a rotary cutting head on which there is mounted one or more cutter elements or bits that are advanced into engagement with the workpiece by advancing the cutting head along a central mandrel that supports the cutting head for rotation about and axial movement along the mandrel. The mandrel is secured to the workpiece by expandable or otherwise moveable workpiece engaging or locking elements that can be actuated by a tool operator to immobilize the tool relative to a tubular workpiece. Typically, in the case of pipe workpieces, the workpiece engaging elements are radially moveable blades or pins that frictionally engage the interior or exterior of a workpiece to lock the workpiece and tool together so that the cutting head can be precisely located relative to the end of the workpiece and manipulated to perform a machining operation, such as beveling or otherwise shaping the end of the workpiece in preparation for a subsequent welding procedure involving the workpiece.
In prior art devices of this kind, the drive motor is usually integrated with or connected to the tool such that the motor may drive the cutting head in rotation while the reaction torque between the cutting head and the motor is reacted back into the mandrel that is affixed to the workpiece. Various torque reacting schemes are described in the prior art to avoid reaction torque between a driving motor and a cutting head causing relative rotation between the motor (or the tool drive train) and the cutting head.
More recently, the use of single modular drive motor units, each including a driving head for engaging and driving various machine tools, including pipe end preparation tools, interchangeably with each other has become significant. In such arrangements, the driving head of the drive motor unit contains rotatable torque transmitting elements that are intended to engage rotary drive transmitting members on the various machine tools which enables the tools to be interchangeably used with a singular modular drive motor unit. This presents a problem, however, in reacting driving torque between a rotary cutting head of a portable machine tool driven by such a drive motor unit and the drive motor unit itself. Since the drive motor unit is a separate module that is quickly connectable and separable from the machine tool body, typical torque reacting schemes are not appropriate to restrain relative rotation between the drive motor unit and the mandrel shaft that is secured relative to the tubular workpiece.
The present invention is intended to solve this problem and to provide a portable machine tool for preparing pipe ends for welding that is compact, convenient to use, and can be utilized with a modular drive motor unit of the type described while restraining torque reaction movement of the drive motor unit relative to the mandrel shaft during operation of the tool.